1. Field of the Invention
The present invention relates to a machine tool that cuts a workpiece and a machining method.
2. Description of the Related Art
A lathe, which is a machine tool, holds a workpiece to be machined, on a rotating shaft (spindle) and performs cutting or the like on the workpiece using a cutting tool while rotating the workpiece. As a machining method using a lathe, for example, there is known a machining method of cutting a workpiece while feeding a cutting tool in a tangential direction of the workpiece (a direction crossing the rotation axis (see Japanese Patent No. 3984052).
In this machining method, the edge of the cutting tool is positioned so as to be inclined with respect to the direction of a generating line of the cut portion of the workpiece by a predetermined angle. As the predetermined angle is reduced, the edge of the cutting tool comes closer to a state in which the edge is along the generating line of the workpiece. Accordingly, the cutting range in the direction of the generating line is widened, resulting in a reduction in the machining time. However, if a small-diameter workpiece, for example, is cut over a wide range thereof, the load on the workpiece (the cutting force applied to the workpiece) is increased. Thus, chattering vibration, bending, or the like may occur in the workpiece. For this reason, it is necessary to adjust the direction of the edge (edge angle) to reduce the load on the workpiece. A conventional machine tool is provided with multiple types of cutting tools or holders having different edge angles with respect to a generating line of a workpiece, and the operator replaces the cutting tool or holder with another to change the direction of the edge.
However, the method of replacing the cutting tool or holder has a problem that the operator has to do troublesome work such as demounting and mounting of the cutting tool or the like and this work takes time.